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CODE OF LIGHTING 
SCHOOL BUILDINGS 



Copyright 1918 by 

ILLUMINATING ENGINEERING SOCIETY 

29 Wert 39th Street, New Yofk, N. Y. 



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CODE OF LIGHTING 
SCHOOL BUILDINGS 



Copyright 1 9 1 8 by 

ILLUMINATING ENGINEERING SOCIETY 

ii 

29 West 39th Street. New York, N. Y. 






MAV 2\ ISI8 



• CLA500081 



PREFACE. 



There are 20,000,000 school children in the United States 
who are devoting several hours each day to study or to the per- 
formance of other work equally trying to the eyes. According 
to the available statistics nearly 10 per cent, of the number of 
school children examined are found to have defective vision. 

The severe requirements imposed upon children's eyes by mod- 
ern educational methods create need for the best of working 
conditions. Among these conditions lighting is of first import- 
ance. Improper lighting causes eye-strain, resulting in functional 
disorders, near-sightedness and other defects of the eyes. 

The following Code of Lighting School Buildings has been 
prepared by committees of the Illuminating Engineering Society 
in order to make available authoritative information for legisla- 
tive bodies, school boards and others who are interested in enact- 
ments, rules and regulations for better lighting. 

The requirements of the code as set forth in the Articles, are 
based upon good practice at the present time. Standards of illu- 
mination and other requirements are subject to revision by the 
Society with advances in the art of lighting. 

While the code is intended primarily as an aid in formulating 
legislation relating to the lighting of school buildings, it is also 
intended for school authorities as a guide in individual efforts 
to improve lighting conditions. 

Acknowledgment is made of the valuable co-operation of many 
members and non-members of the Society in the preparation of 
this code. 

Further information on this subject may be obtained by ad- 
dressing the Illuminating Engineering Society, 29 West 39th 
Street, New York, N. Y. 



CODE OF LIGHTING SCHOOL BUILDINGS. 



Article I. General Requirements. — When in use, all buildings 
should be provided, during those hours when daylight is inade- 
quate, with artificial light according to the following Articles. 

Buildings hereafter constructed should be so designed that the 
daylight in the work space is reasonably uniform and the dark- 
est part of any work space is adequately illuminated under nor- 
mal exterior daylight conditions.^ 

Article n. Intensity of Artificial Ulumination. — The desir- 
able illumination to be provided and the minimum to be main- 
tained are given in the following table :- 

Desirable and Minimum Illumination. 

Artificial lighting 

Foot-candles (Lumens per square foot)* 

At the work 

Minimum Ordinary practice t 

Storage spaces 0.25 0.5- 1.0 

Stairways, corridors 0.5 1.0-2.5 

Gymnasiums 10 2.0- 5.0 

Rough shop work 1.25 2.0-4.0 

Auditoriums, assembly rooms 1.5 2.5- 4.0 

Class rooms, study rooms, libraries, labora- 
tories, blackboards 3-0 35- 6.0 

Fine shop work 3-5 4-0- 8.0 

Sewing, drafting rooms S-O 6.0-12.0 

Article III. Shading of Lamps. — Lamps should be suitably 
shaded to minimize glare. Glare, either from lamps or from un- 
duly bright reflecting surfaces, produces eye-strain. 

* It should be borne in mind that intensity of illumination is only one of the factors 
on which good seeing depends. 

t Under the column headed "Ordinary practice," the upper portion of the range of in- 
tensities is preferable to the lower; where economy does not prohibit, even higher in- 
tensities than those cited are often desirable. 

1 Daylight illumination values should be at least twice the values given in the Table 
Article II, for artificial lighting. 

» The illumination intensity should be measured on the important plane which may 
be the desk-top, blackboard, etc. 

The method of computing the flux of light (lumens) required to do any desired illu- 
mination is described under the heading "Design of I,ighting Installation" on page 12. 

For more specific information regarding the lighting of shops, see ''Code of Lighting 
Factories, Mills and Other IVork Places", issued by the Illuminating Engineering Society. 



6 CODE OF IvIGHTiNG SCHOOIv BUILDINGS 

Article IV. Distribution of Light on the Work. — Lamps should 
be so arranged as to secure a good distribution of light on the 
work, avoiding objectionable shadows and sharp contrasts of in- 
tensities. 

Article V. Color and Finish of Interior. — Walls should have a 
moderate reflection factor; the preferred colors are light gray, 
light buff, dark cream and light olive green. Ceilings and friezes 
should have a high reflection factor; the preferred colors are 
white and light cream. Walls, desk-tops and other woodwork 
should have a dull finish. 

Article VI. Switching and Controlling Apparatus. — Basements, 
stairways, store rooms, and other parts of the building where 
required, should have switches or controlling apparatus at point 
of entrance. 

Article VII. Emergency lighting. — Emergency lighting 
should be provided at main stairways and exits to insure reliable 
operation when, through accident or other cause, the regular 
lighting is extinguished. 

Article VIII. Inspection and Maintenance. — All parts of the 
lighting system should be properly maintained to prevent deter- 
ioration due to dirt accumulation, burned-out lamps and other 
causes. To insure proper maintenance, frequent inspection 
should be made at regular intervals. 



NOTEIS — Data and Recommendations. 

DAYLIGHT. 

Intensity of Daylight. — In general, the minimum intensities of 
daylight illumination should be considerably greater than those 
provided in artificial lighting, owing to the adaptation of the eye 
to a much higher level of illumination (brightness) in the day- 
time. 

Direction of Light. — One of the fundamental rules for proper 
lighting of desks is to have the preponderance of light come from 



code; of IvIGhting school buildings 



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PLAN. 
Fig. I.— Unilateral daylighting. Scaled drawing of a typical modern class room. 



8 CODE OF LIGHTING SCHOOI, BUII^DINGS 

the left side. For this reason many school authorities advocate 
unilateral lighting, that is, lighting by windows located on one side 
of the room only, especially for class rooms (see Fig. i). This 
method of lighting is recommended where the rooms do not ex- 
ceed about 24 ft. (7.9 m.) in width, with windows about 12 ft. 
(3.9 m.) high. If the rooms are much wider than this, bilateral 
lighting, that is, lighting by windows located on two sides of 
the room, may be required in order to provide sufficient illumina- 
tion in every part of the room and at the same time to prevent 
too great a diversity of contrast in the intensity of light on the 
work spaces. 

To secure the highest lighting value it is recommended that 
the room be so designed that no working location is more distant 
from a window than one and one-half times the height of the top 
of the window from the floor. 

Windows at the left and rear where practicable are preferable 
to those on the left and right sides of the room, because of cross 
shadows created by the latter arrangement. Lighting by over- 
head sources of natural illumination although sometimes used 
for assembly rooms, auditoriums and libraries, with relatively 
high ceilings, has ordinarily little application in class rooms and 
has found little favor in practice. 

The sky as seen through a window is a source of glare. For 
this reason the seating arrangements should always be such that 
the occupants (pupils) of the room do not face the windows. 

Window Openings. — Tests of daylight in well lighted school 
buildings indicate that, in general, the glass area does not fall 
below 20 per cent, of the floor area. 

As the upper part of the window is more effective in lighting 
the interior than the lower part, it is recommended that the win- 
dows extend as close to the ceiling as practicable. 

Lighting Value of a Window. — The lighting value of a window 
at any given location in the room, will depend upon the bright- 
ness of the sky, the amount of sky visible through the window at 
the given location in the room, and indirectly upon the reflection 
factor of the surroundings and the dimensions of the room. 

Observations in well lighted school rooms having a compara- 
tively unobstructed horizon, show that under normal conditions 



CODE OF LIGHTING SCHOOL BUILDINGS 9 

of daylight, satisfactory illumination is usually obtained when 
the visible sky subtends a minimum vertical angle of 5° at any 
work point of the room. 

In cases in which the horizon is obstructed, as by adjacent high 
buildings or by high trees, provision should be made for a larger 
window area than would otherwise be required; also if need be, 
for redirecting the light into the room by means of prismatic 
glass in the upper sashes of the windows, or by prismed canopies 
outside of the windows. 

Window Shades. — Although direct sunlight is desirable in in- 
teriors from a hygienic standpoint, it is often necessary to exclude 
or diffuse it by means of shades. These shades should perform 
several functions, namely, the diffusion of direct sunlight, the 
control of illumination to secure reasonable uniformity, the elimi- 
nation of glare from the visible sky and the elimination of glare 
from the blackboards wherever possible. These requirements 
make it desirable to equip each window, especially in class rooms, 
with two shades operated by double rollers placed near the level 
of the meeting rail. The window shades may thus be raised or 
lowered from the middle, which provides the maximum elasticity 
for shading and diffusing the light. The shades should be prefer- 
ably of yellow-colored material that is sufficiently translucent to 
transmit a considerable percentage of the light while at the same 
time diffusing it. 

A more complete control of the light may be obtained by the 
use of two independent sets of shades at each window. Where 
two sets of shades are used, one should be preferably a very dark 
green of heavy material that will exclude the light entirely, and 
the other preferably a yellow-colored material as above described. 

Different views of a window equipped with a single set of ad- 
justable shades as used in the public schools of New York City 
are shown in Fig. 2. It will be noted that this method of in- 
stallation permits of lowering the window from the top or raising 
it from the bottom without interference with the shades. 

Light Courts. — Reflection of light from the walls of courts is 
very helpful in increasing interior illumination. Hence the walls 
of courts should have high reflection factors. Dark colors should 
be avoided. 



lo code; of lighting school buildings 

Maintenance. — Windows and overhead sources of natural light 
(so-called skylights) should be washed at frequent intervals and 
surfaces such as ceilings and walls should be cleaned and refin- 
ished sufficiently often to insure their efficiency as reflecting sur- 
faces. It should be borne in mind that the maintenance of ade- 
quate daylight indoors is also dependent upon various external 
factors, such as the future erection of buildings and the growth 
of trees or vines. 

ARTIFICIAL LIGHT. 

Systems of Xighting. — It is customary to divide the systems of 
artificial lighting into three classes, namely, direct, semi-indirect, 
and indirect. This division is arbitrary and the boundary lines 
are quite indefinite. 

A direct lighting system is known as one in which most of 
the light reaches the work plane directly from the lighting 
unit including the accessory which may be an opaque or glass 
reflector or a totally enclosing transparent or translucent envelope. 
Direct lighting systems may be further classified as localized and 
general or distributing. In the former the units are so placed 
as to light local work spaces, and in the latter they are well 
distributed so as to light the whole area more or less uniformly. 

A semi-indirect system, is know^n as one in which a portion of 
the light reaches the work plane directly from the unit and a 
relatively large portion reaches the work plane indirectly, by 
reflection from the ceiling and walls. The accessory is usually 
an inverted diffusing bowl or glass reflector. When this glass 
has a high transmission factor the lighting effect approaches that 
of ordinary direct lighting, and when of low transmission, the 
effect approaches that of indirect lighting. 

An indirect system is known as one in which all or practically 
all the light reaches the work plane indirectly after reflection 
from the ceiling and walls. The accessory is usually an opaque 
or slightly translucent inverted bowl or shade containing a re- 
flecting medium. 

All three of these systems of lighting (illustrated in Figs. 3, 4, 
and 5) are in successful use in schools. There has been a grow- 
ing preference for semi-indirect and indirect lighting, especially 
since the introduction of modern lamps of great brilliancy. Local 
lighting by lamps placed close to the work is unsatisfactory ex- 




Fig. 3. — Good direct lighting. 
In general, semi-indirect or indirect lighting is better for .school rooms. 




Fig. 4. — Good indirect lighting. 




Fig. 5 — Good semi-indirect lighting. 




Kig. 6. — Bad lighting. The lighting units are hung too low and the light sources are not 
adequately shaded. Note the glossy varnished surfaces on benches and woodwork. 




Fig. 7.— Bad lighting. The local lamps, if used at all, should be provided with 

reflecting shades to protect the eyes from glare and at the same time to 

direct the light to the work. General illumination by 

overhead units is preferable. 




8.— Bad lighting. The use of local lighting by adjustable table lamps usually 
results in glare from lamps on neighboring tables; also in annoying 
shadows. The difficulties may be overcome by the use 
of a system of general illumination. 



CODE OF LIGHTING SCHOOL BUILDINGS II 

cept for special cases such as the lighting of blackboards, maps, 
charts, etc. Examples of bad lighting are shown in Figs. 6, 7, 
and 8. 

Shading of Lamps. — Except in very rare instances bare light 
sources should not be exposed to view. They should always be 
adequately shaded or completely hidden. Even when shaded by 
translucent media, such as dense glassware, the lighting units 
should be placed well out of the ordinary range of vision; in 
other words it is recommended that lighting units be of low 
brightness,^ even if they are located high in the field of view. 

The maximum brightness contrast of juxtaposed surfaces in the 
normal visual field should be preferably not greater than 20 to 
I ; that is to say, the darkest part of the work space observed 
should have a brightness preferably not less than one-twentieth 
of that of the brightest part. 

Glossy Surfaces and Eye-Strain. — Glossy surfaces of paper, 
woodwork, desk-tops, walls and blackboards are likely to cause 
eye-strain because of specular or mirror-like reflection of images 
of light sources, especially when artificial light is used. Matte 
or dull finished surfaces are recommended. It is to be noted that 
a high reflection factor does not necessarily imply a polished or 
glazed surface. 

To minimize eye-strain it is recommended that unglazed paper 
and large plain type be used in school books. 

• Preferably not to exceed 250 tnillilamberts. A millilambert is equal to the bright- 
ness of a perfectly reflecting and diffusing surface illuminated to an intensity of 0.929 
foot-candle, (0.^29 lumen per square foot). It is also equal to 0.002 candle per square inch. 

The foMowing table shows the order of magnitude of the brightness of some light 
sources in common use: 

Approximate brightness 



Indirect lighting: ceiling, directly above the light- 
ing unit 

Semi-indirect lighting: heavy density glassware . 
" " " light density glassware . . 

Direct lighting: 10 in. (25 cm.) opal glass ball con- 
taining loo-watt vacuum tungsten 

lamp at center 

" " vacuum tungsten lamp, (frosted) 

in open bottom reflector .... 

Vacuum tungsten lamp, filament exposed to view . 

Gas-filled tungsten lamp, filament exposed to view 

Gas-mantle, bare 

" " concealed in 6 in. (15 cm.) opal glass 

globe 1,000. 2. 

Mercury arc tube (glass) 8,000. 16. 

Daylight: clear blue sky i,ooo. 2. 



Millilamberts 




Candles 
per sq. in. 


5- to 75. 




o.oi to 0.15 


35. to 100. 




0.07 to 0.2 


200. to 1,000. 




0.4 to 2.0 


250. to 500. 




0.5 to I.O 


2,000. to 3,000. 




4. to 6. 


500,000. 


I, 


,000. 


2,000,000. 


4 


,000. 


15,000. 




30. 



12 CODE OF UGHTING SCHOOL BUILDINGS 

Children should be taught to hold their books properly, to as- 
sume a correct position relative to the light source, and to safe- 
guard their vision. 

Color of Light. — It has been found in practice that the admix- 
ture of daylight and artificial light is not satisfactory unless the 
latter is derived from lamps designed with special reference to 
producing daylight color values. Hence in w^aning daylight it 
is desirable to shut out the daylight and to use artificial light 
exclusively unless the lamps are of the type mentioned. 

Design of Lighting Installation. — The illumination intensity on 
the horizontal v^ork plane should be as uniform as possible. The 
variation should not be greater than 4 to i.'* 

Approximate Coefficients of Utilization— Modern Lighting 

Equipment. 

Small Rooms (Offices, Corridors, etc.). 

I,ight color Medium color 

walls walls 

l,ight color ceiling Light color ceiling 

Direct lighting; dense glass (open bottom 

reflectors) 0.40 0.3S 

Semi-indirect lighting; dense glass c.25 O.22 

Indirect lighting 0.23 0.20 

Medium Sized Rooms (Class Rooms, Laboratories, etc.). 
Direct lighting; dense glass (open bottom 

reflectors) 0.50 0.4S 

Semi-indirect lighting ; dense glass 0.35 0.30 

Indirect lighting 0.30 0.25 

Large Rooms (Auditoriums, etc.). 
Direct lighting; dense glass (open bottom 

reflectors) 0.62 0.60 

Semi-indirect Ughting ; dense glass 0.43 0.40 

Indirect lighting 0.40 0.38 

The chief factors which must be considered in arriving at the 
size and number of lamps to be used in a given room are ( i ) the 
floor area; (2) the total luminous flux^ emitted per lamp, and 

* This ratio refers to the light received by the object illuminated and should not be 
confused with the ratio of 20 to i for brightness contrast previously given on page 10, 
which refers to the light radiated by the object. For example, a blackboard and a white 
sheet of paper on it may receive the same amount of light, but the latter will reflect 
much more light than the former, thus causing a marked brightness contrast between 
the two surfaces. 

6 The flux is measured in lumens. A lumen is the unit of light flux and is the quan- 
tity of light required to illuminate i square foot of area to an average intensity of i foot- 
candle. 



CODE OF UGHTING SCHOOL BUILDINGS 13 

(3) coefficient of utilization of the particular system considered. 
The first should be measured in square feet. The second may be 
obtained from a data book supplied by the manufacturers of 
lamps. The third involves many factors such as the relative di- 
mensions of the room, the reflection factor of the surroundings, 
the number of lighting units and their mounting height, and the 
system of lighting. By coefficient of utilisation is meant the pro- 
portion of the total light flux emitted by the lamps which is ef- 
fective on the work plane. In the accompanying table ap- 
proximate coefficients of utilization for modern lighting equip- 
ment are given. The work plane in this case is a horizontal 
plane 30 in. (76 cm.) above the floor. These values refer to 
the initial installation without any allowance for depreciation. 

For determining approximately the size and number of lamps 
to be used in a given room by means of the coefficients of utiliza- 
tion given in the preceding table, it is necessary to know the lumi- 
nous output in lumens per watt for the electric lamps considered 
or in lumens per cubic foot of gas consumed per hour if gas lamps 
are considered. At the present time (191 7) the light output of 
tungsten filament electric incandescent lamps, based on average 
service conditions of regularly maintained installations, ranges 
from 8 lumens per watt for the smaller vacuum tungsten lamps 
to 14 lumens per watt for the larger gas-filled tungsten lamps em- 
ployed in school lighting. For incandescent gas systems similar 
service values range from 150 to 250 lumens per cubic foot of 
artificial gas consumed per hour. The computation for the total 
lumens required to give a certain illumination intensity in foot- 
candles is as follows: 

N = number of lamps. 

L, = lumens output per lamp. 

E = coefficient of utilization. 

A = area of floor or horizontal work plane in square feet. 
I = illumination intensity in foot-candles. 
N X LXE ^ 

A 
that is, the number of lamps multiplied by the output per lamp 
in lumens, multiplied by the coefficient of utilization, divided by 
the area of the horizontal work plane in square feet, gives the 
illumination intensity in foot-candles. 



14 CODE OF UGHTING SCHOOL, BUILDINGS 

If the size of the lamps is to be ascertained the computation 
is made thus : 

^ I X A 
^ NXK 
To illustrate by an example, assume a room, whose floor (also 
work plane) is 30 ft. by 18 ft. (9.1 by 5.5 m.), to be lighted 
by a semi-indirect system from six fixtures containing one lamp 
each. It will also be assumed that the ceiling is highly reflecting, 
the walls moderately reflecting, and the illumination intensity de- 
sired is 5 foot-candles. The luminous output required of each 
of the six lamps will be found by substituting the assumed values 
in the equation, thus : 

5 X 30 X 18 , 

L = = I , SCO lumens 

6 X 0.30 '^ 

Allowing a depreciation factor of 20 per cent, as representing a 
well maintained installation, the lumens actually required would 

Ije h^^ = 1,875 lumens. If gas-filled tungsten lamps are con- 
0.8 

sidered, whose average output under service conditions is 12 

lumens per watt, it is seen that a 150- watt lamp in each fixture 

will give the desired results. 

If gas mantle lamps are considered, whose average output in 
lumens under service conditions is 250 lumens per cubic foot of 
gas consumed per hour, it is seen that a lamp consuming 5 cubic 
feet of artificial gas per hour will be satisfactory in each fixture. 

The above example is intended solely to illustrate the method 
of computation. Estimates of the illumination intensity obtained 
from an actual installation may also be made by a similar com- 
putation. 

Suitable switching and controlling arrangements should be 
made to permit of lighting one or more lamps independently as 
conditions may require. 

The teacher's desk may be illuminated by one of the overhead 
lighting units, or if necessary, by a desk lamp. 

With the usual lighting equipments the distance between the 
units should not exceed one and one-half times the height of the 
apparent source of illumination above the working level. 



CODE OF LIGHTING SCHOOL BUILDINGS 



IS 



Blackboards. — Blackboards should be of minimum size prac- 
ticable and should not be placed between windows. Their posi- 




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Fig. g. — Diagrammatic illustration of glare from blackboards, 
(a) Showing that occupants of seats in shaded area are subjected to daylight 

glare from blackboards. 

(i) Showing angles at which glare is experienced from daylight and from 

artificial light. 

(c) Arrangement of local artificial lighting to minimize glare. 

tion should be carefully determined so as to eliminate the glare 
due to specular reflection of images of either artificial or natural 
light sources directly into the eyes of occupants of the room. 
The surface of blackboards should be as dull as possible and this 
dullness should be maintained. 



i6 



CODE OF LIGHTING SCHOOL BUILDINGS 



Glare, due to specular reflection from blackboards, may be re- 
duced or eliminated by lighting them by means of properly placed 
and well shaded local artificial light sources. 

In Fig. 9 are shown some simple graphical considerations of 
blackboard lighting. In (a) is shown a plan view of a room with 
windows on one side. Rays of light are indicated by A, B and 
C in a horizontal projection. These are supposed to come from 
bright sky. By the application of the simple optical law of re- 
flection — the angle of incidence is equal to the angle of reflection 
— ^it is seen that pupils seated in the shaded area will experience 
glare from the blackboards on the front wall. In (&) is shown 
the vertical projection of the foregoing condition. It will be ap- 
parent from this graphical illustration that by tilting the black- 
board away from the wall at the top edge, the pupils in the back 
part of the room will be freed from the present glaring condition. 
Whether or not this tilting will remedy bad conditions may be 
readily determined in a given case. In (&) the effect of specular 
reflection of the image of an artificial light source is shown by 
D. In (c) is shown a proper method of lighting blackboards by 




Fig. 10 (a). — Old artificial lighting equipment. 

means of artificial lighting units. This will often remedy bad 
daylight conditions whether due to an insufficient illumination in- 
tensity of daylight or due to reflected images of a patch of sky. 

In order to avoid excessive brightness contrast which is try- 
ing to the eyes, blackboards should not be placed on a white or 
highly reflecting wall. 

Rehabilitating the Lighting of Old Buildingfs. — This will be il- 
lustrated by an actual case where the artificial lighting of a class 



CODE OF LIGHTING SCHOOL BUILDINGS 



i7 



room was made satisfactory at a small expense. In Fig. lo (a) 
is shown an elevation of a section of the class room showing the 
old fixtures. In Fig. lo (c) the circles containing crosses (^) 
indicate the positions of the two old fixtures in this room. The 
chief objections to this old system were as follows: 

(i) The lighting units were hung too low, so that eye-fatigue 
resulted from the bright sources in the visual field. 



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class room. 



i8 code; of lighting school buildings 

(2) The light sources were not shielded from the pupils' eyes. 

(3) Two fixtures are insufficient to provide satisfactory il- 
lumination over the entire work plane in a room of the dimen- 
sions shown. This unsatisfactory condition was remedied by 
means of six fixtures placed as indicated by the circles (]2^) in 
Fig. 10 (c). 

These fixtures, shown in elevation in Fig. 10 (&), consisted of 
inverted diffusing glass shades containing one lamp each. The 
dimensions of the room are shown in the illustration. 

Maintenance. — A systematic maintenance should be provided 
in order to insure against depreciation in the illumination inten- 
sity due to burned-out lamps, broken gas mantles, discoloration, 
etc., and to accumulations of dirt upon the lamps, and upon the 
surfaces of the reflecting and transmitting media. It is found in 
practice that carelessness in this respect may easily reduce the 
effective illumination by 50 per cent., especially in indirect and 
semi-indirect lighting. 

Issued Apiil 30, 1918. 



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